The present invention relates to an image forming apparatus capable of preventing generation of image noise by controlling creep of movable members having flexibility such as intermediate transfer belts for use in copying machines and printing machines.
In image forming apparatuses such as copying machines and printing machines, movable members having flexibility such as intermediate transfer belts have conventionally been used. Such movable members possibly suffer creep that is the increase of a strain with a lapse of time under the action of constant external force. The creep has dependence on curvature deformation degree, temperature, curvature deformation state retention time, and material properties of the movable members. Accordingly, in order to prevent the creep of the movable members, improvement of their materials are generally conducted, and if that measure alone is not sufficient, made are such attempts as decreasing the deformation degree of the movable members and/or controlling temperature rise thereof.
However, the trend of image forming apparatuses in recent years is toward downsizing, and so a space inside the apparatus becomes small. Consequently, the movable members set in the apparatus are often disposed in the state of having a high deformation degree, which is counted as a disadvantage with respect to creep. For example, a roller which supports an intermediate transfer belt that is a movable member having flexibility from therewithin is, for example, 30 mm in diameter in the case of a conventional model, whereas the roller is, for example, 24 mm in diameter in the case of a recent model. Thus, decreasing the diameter of the roller achieves space saving, which, however, causes the intermediate transfer belt to be supported in the state of being curvature-deformed with a curvature larger than a conventional one. With such a large curvature, creep tends to be generated in a portion of the intermediate transfer belt supported in the state of being curvature-deformed under the action of predefined tension, and when creep deformation is increased, image noise is generated in that portion.
Generally, the creep is highly dependent on temperature, so that the inside of the apparatus and the intermediate transfer belt are cooled by means of a fan in order to cope with the creep while maintaining space-saving achievement. However, the use of the fan itself is discontinued in most cases in light of cost saving in these days, which works against solving the problem of the creep generated in the movable members having flexibility in terms of temperature.